1. Field of the Invention
This invention relates to a rigid vinyl chloride resin composition having good impact strength and fluidity or flowability.
2. Description of the Prior Art
Impact-resistant rigid vinyl chloride resin moldings in which impact-resistant improvers such as ABS resins or MBS resins are added to vinyl chloride resins are widely used as pipings, building materials, access floor parts and the like. These rigid vinyl chloride resin moldings are manufactured according to molding techniques such as extrusion molding, injection molding and the like.
Where mixtures for rigid vinyl chloride resin moldings which are obtained by adding MBS resins to vinyl chloride resins having an average degree of polymerization of 700 to 800 are injection molded, the molded articles have been ones which are relatively small in size and include, for example, pipes, joints, access floors and the like.
The recent spread of office automation apparatus has urged studies on molding of housings for office automation apparatus made of rigid vinyl chloride resin mixtures in which impact-resistant improvers such as MBS resins or ABS resins are added to vinyl chloride resins.
However, when using rigid vinyl chloride resin mixtures in which impact-resistant improvers such as MBS resins or ABS resins are added to vinyl chloride resins for the injection molding of housings for office automation apparatus, the housings for the OA apparatus are usually so large in size that there arises the problem that the molten resin cannot be uniformly filled throughout a mold upon molding.
There has been a demand for improving the fluidity of a molten resin upon molding.
In order to improve the fluidity, there are known methods including (1) a method using a vinyl chloride resin having a low average degree of polymerization, and (2) a method wherein an amount of an impact-resistant improver is reduced. Although the fluidity is improved in both methods (1) and (2), they are disadvantageous in that the resultant moldings lower in tensile strength and impact resistance. Accordingly, there is a demand for a method of improving fluidity of a molten resin in the course of molding without a sacrifice of tensile strength and an impact resistance of moldings.
Japanese Laid-open Patent Application No. 3-134045 proposes a rigid vinyl chloride resin composition comprising a vinyl chloride resin and an impact-resistant improver wherein an acrylonitrile-styrene copolymer having a weight ratio of acrylonitrile and styrene of 20/80 to 40/60 is added to the composition. As a result, the molten resin melt obtained therefrom can be improved in fluidity upon molding without impeding tensile strength and impact strength of the resultant moldings.
However, although the fluidity of the molten resin upon molding can be improved, the above demand is not fully satisfied.